More and more people are growing avocados from discarded pits. However, in most parts of the United States, growing an avocado tree isn’t as easy as these social media claims suggest. If yours is showing signs of dying, you’ll want to read this.
The most common causes of an avocado tree dying are diseases, pests, and cultural problems. Some of these problems are preventable, some are solvable, but some are simply a sign that your area is not conducive to growing avocado trees.
Here’s are the most common causes and some helpful preventative solutions.
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Like all fruit trees, avocados are susceptible to many diseases. Fortunately, many of these diseases are minor and do not lead to long-term problems for the tree. However, there are three in particular that can cause dieback or death:
- Avocado Black Streak
- Phytophthora Canker (collar rot)
- Armillaria Root Rot (oak root fungus)
Avocado Black Streak
Avocado Black Streak (ABS) is a common problem for Guatemalan cultivars like Hass and Reed. It is caused by an unknown bacteria, and presents with the following symptoms:
- Poor growth
- Yellowing leaves
- Decreased fruit production
- Cankers on trunks and branches
- Sudden death of new growth
Cankers that exude a dry, chalky sugar are the surest sign that your tree has ABS. When the cankers are removed, the tissue underneath is discolored, usually a mix of reddish-brown and black, which indicates that some of the tissue has already died (source).
ABS is an unpredictable disease. Some trees that have it may linger for years; others may collapse suddenly.
Because no one is sure which organisms cause ABS, there are no chemical solutions.
However, what experts do know is that ABS only seems to affect avocado trees that are already stressed. This means that the best way to prevent and treat ABS is to maintain consistent watering and fertilizing practices.
Phytophthora Canker (Collar Rot)
Phytophthora canker is one of the most serious avocado tree diseases. The primary symptom is cankers that appear at or just below ground level on the tree’s trunk.
Unlike ABS, these cankers let out a reddish sap that covers an orange-brown lesion. Eventually, the disease spreads to the tree’s major roots, significantly impairing them (source). If left unchecked, phytophthora canker will kill your avocado tree.
Organisms in the Phytophthora genus thrive in wet conditions, so phytophthora canker is most common in soils that drain poorly or where trees are over-watered. Cankers will also grow more rapidly if the trunk is wounded in some way (source).
Some fungicides may be helpful, but check with your local Extension agent or tree expert as not all fungicides are available everywhere.
Even with the use of fungicide, prevention is the best control method. Plant in well-drained soils, and avoid getting the lower trunk of your tree wet. Avoid mechanical injury to your tree’s trunk (source).
Armillaria Root Rot (Oak Root Fungus)
A soil fungus is the cause of armillaria root rot. By the time you see above-ground symptoms, infection in the roots is already underway. The above-ground symptoms include:
- Yellowing and wilting leaves
- Limb and leaf dieback
- Mushrooms growing around the tree’s base
If a young avocado tree is infected, it will probably die quickly. A mature tree may be able to rally after an infection, but will eventually succumb when the fungus takes over the root system (source).
Again, prevention is the best control. Avoid planting your avocado tree on sites where oaks, citrus trees, or other susceptible trees once grew. Remove all parts of a dead avocado tree from the soil and clean your equipment thoroughly to prevent the fungus from spreading.
Avocados attract a variety of insects and pests, but the good news for growers is that most of these are non-fatal.
The one pest to look out for is mites, and even these are only problematic in large numbers.
Persea mites have the potential to do the most damage to your avocado tree. They spread to avocados from weeds, ornamentals, or other susceptible plants grown nearby. Persea mites prefer Hass and Gwen varieties, but they aren’t limited to just those two.
Persea mites feed on leaves’ undersides, leaving brown spots and silver webbing behind. If the mite colony is large enough, it will cause defoliation (loss of leaves), leading to sunburn, dropped fruit, and tree stress.
While you can use pesticides to control mite infestations, this may not be your best option. There are numerous insects that are natural predators of mites, and a pesticide will kill them as well.
Instead, you can prevent a large infestation by avoiding quick-release, nitrogen-heavy fertilizers. Persea mites thrive on the increased nitrogen in the leaves.
You can also use a strong hose to spray mites off leaves if you notice them moving in on your avocado tree.
If diseases and pests don’t seem to be causing your avocado tree’s problems, the culprit may be one of the following:
- Improper site selection and soil
- Temperature and wind
- Irrigation problems
Improper Site Selection and Soil
Avocados require full sunlight, six to eight hours per day on most days. If your tree is suffering, lack of sunlight may be the cause, especially if your tree is located on the north or east sides of structures that keep it shaded.
Avocado trees are also intolerant of poorly drained soils. If water tends to pool in your yard, your soil is not draining to the extent that avocado trees require.
It’s also possible that your soil is too shallow for proper root development. You can compensate for this with good watering practices, but if your soil is shallow and drains poorly (e.g., clay), your tree will not grow well.
Learn more about fruit tree root depth and it’s role in growing a healthy tree.
Temperature and Wind
Avocados cannot tolerate low temperatures for very long. In fact, the Hass variety will suffer damage after only four hours at 30℉. Mexicola is the most cold-tolerant variety, but even then, only to the low 20s.
For most regions of the United States, this makes avocados a non-starter.
Avocados are also prone to defoliation due to wind if they aren’t protected. If your tree is disease and pest-free but still losing quite a few leaves, the wind is a likely culprit.
Overwatering can encourage phytophthora canker, and underwatering can lead to ABS, in addition to the numerous other problems caused by improper irrigation.
In general, avocado trees do not require water every day. Young trees need water more often than mature ones, but even then, you should only be watering a couple of times a week (source).
There is an easy way to test if your tree needs water. Take a handful of soil from the tree’s base and squeeze it into a ball. If the ball of soil crumbles, it’s time to water.
Preparing to Plant and Best Growing Practices
If you live in a region where avocado trees can flourish, there are several steps you can take to help your tree succeed:
- Rootstock selection
- Proper site selection
A number of problems can be avoided with the right rootstock. Some, like Topa Topa, are relatively cold-tolerant; others, like Thomas and Dusa, are resistant to root rot.
Consult a local expert to choose a rootstock that will suit your climate, soil, and desired yields.
Proper Site Selection
Choose a location for your tree where it will receive full sunlight but will still be somewhat protected from the wind. Staking young trees can help secure them from the wind without blocking sunlight.
Your planting location should also be a place that has well-drained soil and won’t collect puddles of water.
Prune young trees to encourage branches to grow laterally. Mature trees should be pruned to stay within 10-15 feet high. This prevents upper branches from blocking sunlight to lower branches, reduces the chance of storm damage, and makes the tree easier to care for. Read our guide on how to prune correctly.
Avocado trees need a balanced fertilizer (6-6-6 or 10-10-10) three or four times a year. However, they also need applications of boron, copper, manganese, and zinc during the growing season.
If your soil is alkaline, you will also need to give your tree iron chelates in late spring or early summer (source).
While diseases and pests are always a risk, you can prolong the life and health of your avocado tree by maintaining good growing practices like proper irrigation, pruning, and fertilization.
If your region is simply too cold for avocados, consider growing cherries, peaches, apples, or one of the many other fruit trees that are successful in cooler climates.
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